Exoplanet Excursions: March 2015

What could be better than an eclipse? An eclipse with added volcanoes, obviously.

Having witnessed two glorious exostellar eclipses in recent excursions, perhaps we ought to complete the trilogy in honour of the hugely anticipated total solar eclipse that’s set to occur over the Faroe Islands on 20 March.

There’s one other variety of eclipse I’m curious to see. Usually eclipses have the ‘black hole’ effect, but what if the eclipse-causing object was a fiercely volcanic world akin to Jupiter’s moon Io? I’ll take a look around the system of Mu Arae in the constellation of Ara, the Altar: hopefully here we should locate such a spectacle.

Mu Arae lies at a distance of 50.6 lightyears from Earth. It isn’t visible from UK skies, but at mag. +5.1 it’s just about visible to the naked eye from the southern hemisphere. There are four planets believed to be orbiting this star, and one of them – Mu Arae b, in the star’s habitable zone – provides exactly what we’re looking for: an innermost moon with a larger neighbouring moon close by.

This is a configuration very similar to Jupiter’s Io. Upon a closer inspection, the gravitational effects on this moon of its passage between planet Mu Arae b and its neighbouring body do indeed cause unending friction and violent volcanic activity. This poor world is squeezed and disrupted on its orbit like an eternally tormented stress ball.

Observing this world gives a sense of indigestion. I steer the Cruiser Globe to the correct position for this moon to eclipse parent star Mu Arae. At confirmation of ‘first contact’ this eclipse begins just like those seen from Earth, with a steadily advancing ‘bite’. As the event progresses, the blackened area appears through my eclipse viewer to be gaining a red hue in places. There is no distinct pattern to this just at the moment, it’s more like a deep red ‘lens flare’ bathing the black void.

Moments before the totality of Mu Arae, the red hue deepens in intensity, and as the stellar corona flashes into view in just the same way as that of our own Sun, there’s a second totality effect which looms forth like a mood lamp with its dimmer gently turned up.

This is a breathtaking exoeclipse to witness, with the wonderful extra dimension of volcanic activity made visible. The light of the totally eclipsed star allows the volcanic activity to shine with the colour of a piece of ironwork beginning to glow red hot in the blacksmith’s forge. Pockets and filaments of glowing redness like squashed, backlit raspberries are scattered across the black disc, resembling a growth of lichen on a stone gatepost.

This vision generates a sound in the imagination like the electrical hum heard beneath a pylon. Meanwhile around the edges, volcanic fountains sear upwards, cousins of the ice fountains of Enceladus, visible next to stellar prominences dotted around the black disc at the two, four, five, seven and 11 o’clock positions. It’s a vision of serene violence against the backdrop of a piercing silvery corona.

Jon Culshaw is a comedian, impressionist and guest on TheSky at Night

This column appeared in the March 2015 issue of BBC Sky at Night Magazine

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